Multi-Stage Debulk and Compaction of Thick Composite Repair Laminates

ABSTRACT

A method for fabricating a repair laminate for a composite part having an exposed surface includes applying a release film to the exposed surface and forming an uncured ply stack assembly on the release film. The uncured ply stack assembly is formed by forming and compacting a series of uncured ply stacks. The release film and ply stack assembly is then removed from the exposed surface. A bonding material is then applied to the exposed surface, and the uncured ply stack assembly is applied to the bonding material. The ply stack assembly and bonding material are then cured.

This application is a divisional of U.S. patent application Ser. No.13/776,816 filed 26 Feb. 2013, titled “MULTI-STAGE DEBULK AND COMPACTIONOF THICK COMPOSITE REPAIR LAMINATES”, which is a continuation of U.S.patent application Ser. No. 12/742,603 filed 12 May 2010, titled“MULTI-STAGE DEBULK AND COMPACTION OF THICK COMPOSITE REPAIR LAMINATES,”which is a 371 of P.C.T. Application PCT/US2008/084969 filed 26 Nov.2008, titled “MULTI-STAGE DEBULK AND COMPACTION OF THICK COMPOSITEREPAIR LAMINATES;” which claims the benefit of U.S. Provisional PatentApplication No. 60/990,017 filed 26 Nov. 2007, titled “MULTI-STAGEDEBULK AND COMPACTION OF THICK COMPOSITE REPAIR LAMINATES;” and all ofwhich are hereby incorporated by reference for all purposes as if fullyset forth herein.

BACKGROUND

1. Field of the Invention

The present invention relates to methods of fabricating laminates madefrom polymeric-matrix composite materials.

2. Description of Related Art

Parts made from polymeric-matrix composite materials form manycomponents in modern automotive, aeronautical, and marine vehicles, aswell as components in many other types of equipment and structures. Suchparts may, from time to time, become damaged, thus requiring repair orreplacement. It is often required or at least more cost effective torepair a damaged part than to replace the part. Conventional methods ofrepairing polymeric-matrix composite parts require the use ofspecialized tooling and double vacuum tool/processes, which requiremultiple staging operations and cure cycles, or specialized lay-up toolsand autoclave processing, which is expensive and often impractical whenused to facilitate a repair.

There are many ways to repair damaged polymeric-matrix composite partsthat are well known in the art; however, considerable shortcomingsremain.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the description. However, the invention itself, as well as, apreferred mode of use, and further objectives and advantages thereof,will best be understood by reference to the following detaileddescription when read in conjunction with the accompanying drawings, inwhich the leftmost significant digit(s) in the reference numeralsdenote(s) the first figure in which the respective reference numeralsappear, wherein:

FIG. 1 is an elevated side view of uncured plies applied to a compositepart according to the method of the present application.

FIG. 2 is an elevated side view of a sealing bag enclosing a ply stackon the composite part according to the method of the presentapplication.

FIG. 3 is an elevated side view of multiple ply stacks on the compositepart according to the method of the present application.

FIG. 4 is an elevated side view of a bonding layer disposed between plystacks and the composite part according to the method of the presentapplication.

FIG. 5 is an elevated side view of a sealing bag enclosing multiple plystacks on the composite part according to the method of the presentapplication.

FIG. 6 is an elevated side view of a cured composite layer on thecomposite part according to the method of the present application.

FIG. 7 is an elevated side view of an alternative embodiment of thecomposite part according to the method of the present application.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present invention represents a method for multi-stage debulking andcompaction of thick composite repair laminates made from one or morepolymeric-matrix composite materials. In one embodiment, the method isapplied to the repair of an existing composite part. The method providesa composite part meeting the same laminate quality requirements as athick laminate made using highly-pressurized autoclave processing. Forthe purposes of this disclosure, the term “thick laminate” means alaminate made from more than about 10 plies of polymeric-matrixcomposite material.

Referring to FIG. 1 in the drawings, a pre-existing composite part 101is shown. It should be noted that composite part 101 may be planar ornon-planar in form. A layer of release film 103 is applied to compositepart 101 and a first plurality of uncured plies 105 (only one labeled inFIG. 1 for clarity) of polymeric-matrix composite material is applied torelease film 103. In a preferred embodiment, the number of uncured plies105 making up the first plurality of uncured plies 105 is no more thanabout ten plies. The first plurality of uncured plies 105 makes up afirst ply stack 107. Uncured plies 105 may comprise “wet lay-up” pliesor pre-impregnated, i.e., “pre-preg” plies.

Referring now to FIG. 2, bleeder material (not shown) and a sealing bag201 is applied over first ply stack 107 and release film 103 in aconventional manner. Sealing bag 201 is attached to an exposed surface203 of composite part 101 to create a substantially air tight sealbetween exposed surface 203 and sealing bag 201. A vacuum port 205extends through sealing bag 201 to allow gases to be withdrawn fromsealing bag 201 within the substantially air tight seal between sealingbag 201 and exposed surface 203, A vacuum assembly (not shown) isattached to vacuum port 205, which evacuates gases, as represented byarrow 207, from within the sealed volume of sealing bag 201. In apreferred embodiment, vacuum at a level of two to three inches ofmercury is applied to the sealed volume of sealing bag 201. In additionto applying vacuum, a heat source 209 heats at least first ply stack 107to a desired debulking and compaction temperature. In a preferredembodiment, sufficient heat is applied to first ply stack 107 by heatsource 209 to raise the temperature of first ply stack 107 to atemperature of about 125 degrees Fahrenheit. First ply stack 107 ismaintained at the desired temperature, e.g., about 125 degreesFahrenheit, under vacuum, e.g., about one to two inches of mercury, fora time period sufficient to debulk and partially compact first ply stack107. In a preferred embodiment, first ply stack 107 is maintained at thedesired temperature and under vacuum for about one hour. Subsequently,first ply stack 107 is preferably maintained at the desired temperatureunder full vacuum, e.g., about 28 inches of mercury, for a period oftime of about 30 minutes to further compact first ply stack 107. Afterthe desired period of debulking and compaction time, sealing bag 201,the breather material, and any other ancillary processing materials areremoved from first ply stack 107 and composite part 101. First ply stack107 is now debulked and compacted.

It should be noted that the debulking and compaction temperature is atemperature below a curing temperature of the polymer-matrix compositematerial.

Referring now to FIG. 3, a plurality of ply stacks, such as first plystack 107, a second ply stack 301, and a third ply stack 303, arecombined to form a ply stack assembly 305. Ply stack assembly 305 maycomprise any suitable, desired number of ply stacks, such as ply stacks107, 301, and 303. In the illustrated embodiment, second ply stack 301is formed by applying a plurality of plies, preferably no more thanabout ten plies, to first ply stack 107. A bag, such as sealing bag 201,is then applied to first ply stack 107 and second ply stack 301. Vacuumand heat are then applied to bagged first ply stack 107 and second plystack 301 according to the method described herein concerning FIG. 2.Third ply stack 303, as well as any desired ply stacks in addition tothird ply stack 303, are formed by the same method as second ply stack301.

Referring to FIG. 4, release film 103 (shown in FIGS. 1-3) is removedand replaced with a bonding material 401. Bonding material 401 isdisposed between ply stack assembly 305 and exposed surface 203 ofcomposite part 101. Note that in this one method of bonding ply stackassembly 305 to exposed surface 203. Bonding material 401 also includes,and is not limited to: a layer of adhesive paste or a layer of adhesivefilm disposed between ply assembly 305 and exposed surface 203; and/or,adhesive material disposed within ply stack assembly 305.

As depicted in FIG. 5, bleeder material and a sealing bag 501 is appliedover ply stack assembly 305 and bonding material 401 in a conventionalmanner. Sealing bag 501 is attached to exposed surface 203 of compositepart 101 to create a substantially air tight seal between exposedsurface 203 and sealing bag 501. A vacuum port 503 extends throughsealing bag 501 to allow gases to be withdrawn from sealing bag 501within the substantially air tight seal between sealing bag 501 andexposed surface 203. A vacuum assembly (not shown) is attached to vacuumport 503, which evacuates gases, as represented by arrow 505, fromwithin the sealed volume of sealing bag 501. In a preferred embodiment,full vacuum, e.g., about 28 inches of mercury, is applied to the sealedvolume of sealing bag 501. In addition to applying vacuum, a heat source507 heats at least ply stack assembly 305 to a desired curingtemperature, which is dependent upon the particular composite materialbeing used. In one embodiment, sufficient heat is applied to ply stackassembly 305 by heat source 507 to raise the temperature of ply stackassembly 305 to a temperature of about 250 degrees Fahrenheit. Ply stackassembly 305 is maintained at the desired temperature under full vacuumfor a time period sufficient to sufficiently cure ply stack assembly 305and bonding material 401 to form composite laminate 601, shown in FIG.6. In a preferred embodiment, ply stack assembly 305 is maintained atthe desired temperature and under vacuum for about two hours. After thedesired curing time, sealing bag 501, the breather material, and anyother ancillary processing materials are removed from composite laminate601, as depicted in FIG. 6. The cured ply stack assembly 305 and theprevious composite part 101 now form parts of composite laminate 601, asthe cured ply stack assembly 305 is adhesively bonded to thepre-existing form of composite part 101.

It should be noted that the present method may also be applied to thefabrication of a new composite part, rather than to the repair of acomposite part. For example, composite part 101 may be replaced with alay-up tool. Release film 103 is not replaced with bonding material 401prior to curing ply stack assembly 305, so cured composite laminate 601can be removed from the lay-up tool.

It should also be noted that a damaged composite part 701, shown in FIG.7, may be machined or scarfed to define a recess 703 into which a plystack assembly 705 is received, cured, and adhesively bonded tocomposite part 701 to form composite laminate 707.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the invention.Accordingly, the protection sought herein is as set forth in thedescription. It is apparent that an invention with significantadvantages has been described and illustrated. Although the presentinvention is shown in a limited number of forms, it is not limited tojust these forms, but is amenable to various changes and modificationswithout departing from the spirit thereof.

What is claimed is:
 1. A method for fabricating a laminate for acomposite part, comprising: preparing a lay-up tool for fabricating thecomposite part thereon; applying a release film to the lay-up tool;forming an uncured ply stack assembly that consists of a plurality ofuncured ply stacks, the forming of the uncured ply stack assemblyincluding, for each uncured ply stack: forming the uncured ply stackover the lay-up tool, the ply stack being applied so as to substantiallyconform to the contouring of the lay-up tool, the uncured ply stackconsisting of a plurality of uncured plies; and applying a vacuum andheat below a curing temperature to the thus formed uncured ply stackprior to forming another uncured ply stack over the lay-up tool; whereina first-formed ply stack is applied to contact the release film and therelease film contacts the lay-up tool; and wherein eachsubsequently-formed ply stack is applied to a previously-formed plystack; and curing the uncured ply stack assembly; wherein the first plystack is compacted prior to the subsequent ply stack being applied andsubsequently compacted.
 2. The method according to claim 1, wherein atleast one of the plurality of uncured ply stacks includes one or moreuncured plies comprising polymeric-matrix composite materials.
 3. Themethod according to claim 1, wherein at least one of the uncured plystacks comprises fewer than ten uncured plies.
 4. The method accordingto claim 1, wherein the forming of the uncured ply stack assemblyfurther includes, for each uncured ply stack, at least partiallyenclosing the uncured ply stack within a sealing bag and attaching thesealing bag to the lay-up tool to create an air tight seal around theuncured ply stack.
 5. The method according to claim 4, wherein theapplying of the vacuum includes increasing vacuum pressure within thesealing bag to a first pressure level for a first predetermined amountof time.
 6. The method according to claim 5, wherein the applying of thevacuum includes increasing vacuum pressure within the sealing bag to asecond pressure level for a second predetermined amount of time.
 7. Themethod according to claim 4, wherein the applying of the heat includesincreasing the temperature within the sealing bag to a first temperaturefor a first predetermined amount of time.
 8. The method according toclaim 1, wherein the curing of the uncured ply stack assembly comprises:at least partially enclosing the uncured ply stack assembly within asealing bag and attaching the sealing bag to the lay-up tool to createan air tight seal around the uncured ply stack assembly; increasingvacuum pressure within the sealing bag; and increasing the temperaturewithin the sealing bag to the curing temperature.
 9. A repair laminatefor a damaged composite part having an exposed surface produced by aprocess comprising: preparing a damaged surface on the exposed surfaceof the damaged composite part for fabricating the repair laminatethereon; applying a release film to the damaged surface; forming anuncured ply stack assembly that consists of a plurality of uncured plystacks, the forming of the uncured ply stack assembly including, foreach uncured ply stack: forming the uncured ply stack over the damagedsurface, the ply stack being applied so as to substantially conform tothe contouring of the damaged surface, the uncured ply stack consistingof a plurality of uncured plies; and applying a vacuum and heat below acuring temperature to the thus formed uncured ply stack prior to forminganother uncured ply stack over the exposed surface; wherein afirst-formed ply stack is applied to contact the release film and therelease film contacts the damaged surface; and wherein eachsubsequently-formed ply stack is applied to a previously-formed plystack; removing the release film and the uncured ply stack assembly fromthe damaged composite part; applying bonding material to the exposedsurface; applying the uncured ply stack assembly to the bonding materialon the exposed surface; and curing the uncured ply stack assembly andbonding material; wherein the first ply stack is compacted prior to thesubsequent ply stack being applied and subsequently compacted.
 10. Therepair laminate according to claim 9, wherein at least one of theplurality of uncured ply stacks includes one or more uncured pliescomprising polymeric-matrix composite materials.
 11. The repair laminateaccording to claim 9, wherein the forming of the uncured ply stackassembly further includes, for each uncured ply stack, at leastpartially enclosing the uncured ply stack within a sealing bag andattaching the sealing bag to the exposed surface to create an air tightseal around the uncured ply stack.
 12. The repair laminate according toclaim 9, wherein at least one of the uncured ply stacks comprises fewerthan ten uncured plies.